Soil engineering and principles of soil mechanics have been used for centuries by builders and constructors to enable the construction of well-founded building and structures. Ancient civilizations throughout the world constructed palaces, temples, pyramids, aqueducts and roads that employed foundation preparation and excavations to establish solid footings. Since the beginning of recorded history mankind has known that to build a lasting structure, one must build on a solid foundation.
In 1773 a French physicist named Charles-Augustion de Coulomb published his theories on soil mechanics. He studied the properties of soil use for planning foundations for buildings and highways. A Scottish engineer named William Tankine in 1857 studied how soils react under stress and while being moved during construction. Since these early researches investigated soil-engineering properties, a wealth of knowledge has been amassed to help present day soil engineers safely design foundations and footing for civil construction and building. Standardized testing procedures have been developed to ensure public safety and uniformity in building practices. Most of the test procedures involve physical measurements and testing procedures to assess soil strengths and reactions to imposed loads by constructed structures.
The American Society for Testing and Materials (ASTM) was established in 1898 and has grown to one of the largest voluntary standards development systems in the world. Today ASTM standards are used by thousands of individuals, companies, and agencies. Scientists and engineers use them in their laboratories, architects and design engineers use them in their plans and government agencies reference ASTM standards in codes, regulations, and laws. The ASTM has 132 standards-writing committees. The committee that primarily deals with geotechnical engineering is the Committee D-18 on Soil and Rock. ASTM standards procedures are used and integrated with newly developed soil electrical measuring techniques to enable fast, accurate, and efficient determination of soil properties for civil engineering applications.
Knowing soil density and moisture content is of major importance in the construction of roads and foundations. Proper density and moisture are necessary to prevent premature failure of these constructions. To enable the construction of engineered foundations to meet civil construction specifications soils engineers must conduct geotechnical investigations to determine the character of the soil materials that will be used in the design and construction of the foundations. To properly engineer and design a foundation, the soil characterization is done by both laboratory and field tests that provide strength data that is used in the design calculations for that subject foundation. The routine laboratory test of evaluation of a soil material density is known as the proctor test. The ASTM D-698-00a “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft=lbs/ft3 (600 kN/m3))” or ASTM D-1557-00 “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft=lbs/ft3 (2,700 kN/m3))” are used to determine a soil materials maximum density at an optimum moisture content. Based on the type of foundation that is being designed, a civil engineer can write an engineering specification for the amount of compactive effort that must be applied to the soil to ensure a solid foundation for the given structure. The engineering soil specification will require that the foundation is built and tested to meet some design density criterion at a design moisture content. Field soil density measurements are made physically by a process involving a replacement of a known weight of soil with a measured amount of sand of known and repeatable density. This test is commonly known as the Sand Cone Test. ASTM D-1556-00 “Standard Test Method for Density and Unit Weight of Soil in Place by Sand Cone Method” provides a detailed procedure and protocol of conducting the test. Soil moisture content is measured by determining the weight loss after oven drying. ASTM has several test procedures for determining the moisture content of soil. ASTM D-2216-98 “Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass”; ASTM 4643-00 “Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil by Microwave Oven Heating”; and ASTM 4959-00 “Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil by Direct Heating” are three of the geotechnical industry standards of measuring soil moisture.
In the sand cone test, an amount of compacted soil under test is removed from the construction site, weighed, and the moisture content determined. The hole from which the soil was removed is filled in a prescribed manner with sand of known density. The volume required to fill the hole is measured. The results of these measurements are used to determine the Wet Density, the Moisture Content, and the Dry Density of the soil. These are some of the engineering parameters necessary to determine that the soil construction is adequate for the intended use.
To permit more rapid field measurements of the physical character of the soil, the Nuclear Density Gauge is commonly used in conjunction with the sand cone test. The nuclear density gauge ASTM standard is 2922-96 “Standard Test Method for Density and Soil-Aggregate in Place by Nuclear Method (Shallow Depth”. The sand cone test is used to standardize the nuclear gauge for a specific type of soil, which allows the nuclear gauge to be used repeatedly in the same area on the same type of soil. This permits many more measurements on each site to be made quickly and without continual resort to the cumbersome sand cone test. Nuclear gauges are quite expensive and very costly to have repaired due to the nuclear source they contain. The nuclear density gauge suffers from some degradation of accuracy as a result of not taking care when using it, inclusion of rocks in the measured area, and because the nuclear source changes as a function of radioactive decay. Calibration of the nuclear gauge is costly and required frequently. And, handling of the nuclear gauge is subject to many rules and regulations imposed for the safety of the operators and the general public. Consequently, the nuclear gauge is costly to maintain, and difficult to manage.
One such micro-wave device is described as a density and moisture content measuring invention. (U.S. Pat. Nos. 5,801,537, 5,933,015, and 6,215,317—“Method and apparatus for measuring in-place soil density and moisture content”, all to Siddiqui, et al.). The specifications describe how the volumetric moisture content can be estimated from measurement of the dielectric constant of a test sample of soil. It also infers that gravimetric density can be estimated from the same measurement of dielectric constant, by reference to another laboratory measurement. It is questionable that specific gravity can be measured using dielectric constant only, since in practice, two samples of soil can be prepared that have exactly the same dielectric constant, but have different gravimetric densities and gravimetric moisture contents.
Laboratory testing during the invention of EDG showed that a much higher correlation to the unit weight of water in a soil sample can be achieved using the quotient off measured volume capacitance and measured volume resistance, which is a new and novel feature of the EDG invention.